In the continuous casting of metals, such as steel, the processed metal is cast in a suitable container, called a division tundish, from which it pours in a continuous manner into a casting mould by means of a particular discharge tube known as a nozzle. When steel is cast with relatively large dimensions, the air-steel interface is protected by a powder flux and, under these conditions, during the entire casting operation, the lower end of this nozzle is immersed in the metal contained in the mould.
The following description is based on the case of the nozzle located under the tundish, but this is solely by way of non-limiting example and it should be understood that the invention is concerned with all types of continuous casting nozzles, such as ladle emptying nozzles, division tundish nozzles, or mould nozzles, whether they are in one or a plurality of pieces.
The nozzle is in most cases constituted by a combination of refractory materials whose melting point is particularly high. A nozzle of this type must be resistant not only to the thermal stresses due to the temperature of the cast metal, but also to any chemical action which may result from this, the mechanical effects due to the movements of the metal bath, and erosion by the covering powder generally deposited on the upper surface of the liquid metal in the mould.
In addition, and this is the object of the present invention, it should be protected as far as possible against any blocking, for example by non-metallic inclusions, in particular by alumina or aluminates (in the case of aluminium-killed steel). Blocking of this type is detrimental to the efficiency of the casting operation and impairs the quality of the cast steel, as it requires the deceleration of the withdrawal speed, either for burning off the interior of the nozzle, or for changing the nozzle or the tundish. At worst, casting must be completely stopped.
As far as the inventor is aware, no completely effective method has up to now been proposed to reduce the drawback mentioned above. It is only known to inject inert or neutral gas through the nozzle, which has the effect of retarding its blocking.
The present invention therefore relates to a method of improving the operation of a casting nozzle which has the effect of slowing down the blocking up of the nozzle and making it much less considerable, and therefore reduces or eliminates the drawbacks associated with this.